This invention relates to a transmitting type display device which comprises a transmitting type display panel, such as a transmitting type liquid crystal display panel, illuminated by a built-in light source from the back side to produce a display on the front surface.
In a prior art transmitting type display device, which is provided with no means for controlling the brightness of a built-in light source illuminating the back surface of a display panel, one can see the display on the display panel either easily or with difficulty depending on the intensity of light incident on the front surface of the display panel, i.e., ambient light.
For this reason, brightness control means is provided which controls the brightness of light incident on the back surface of the display panel. In the prior art, however, the brightness control is carried out manually. It is cumbersome, however, to make manual control according to changes in the ambient light or changes in the brightness of a built-in light source.